1. Field of the Invention
The present invention relates to radio link protocols and more particularly to a dynamic data link adaptation for a wireless communication system.
2. Background Information
Layering, or layered architecture is a form of hierarchical modularity that is central to data network design. A layer performs a category of functions or services. All major emerging communication technologies rest on the layers. of the OSI model, illustrated in FIG. 1-a. The OSI model defines a physical layer (Layer 1) which specifies the standards for the transmission medium, a data link layer (Layer 2), a network Layer 3 and application layers (layers 4 to 7).
Physical Layer. The function of the physical layer is to provide a physical pipe, i.e. a communication link for transmitting a sequence of bits between any pair of network elements joined by a physical communication channel. E.g. in the case of wireless networks, this is the channel that physically transports the information between the mobile station (MS) and the base transmission station (BTS), or between the BTS and the mobile switch center (MSC).
Link Layer. Each point-to-point communication link has data link control modules at each end of the link. The purpose of these modules is to exchange information elements (IE), using the physical layer.
Link protocols are a recognized mechanism used within the wired and wireless communications industries to mitigate the effects of impairments introduced by the physical transmission medium. A radio link protocol (RLP) is one that is designed for the wireless environment to deal specifically with the types of impairments found on the radio link between a mobile station (MS) and the radio access network (RAN). The detailed mechanisms employed by an RLP are usually specific to a particular air interface protocol (AIP) and are tailored to the services supported by that AIP. In general, a link protocol may provide mechanisms to deal with errors on the communications link, delays encountered in transmitting information over the communications link, information lost while transmitting over the communications link, bandwidth conservation and contention resolution.
All these AIPs define a limited number of RLPs and select the RLP for a connection during the connection setup phase based on the service requirements. The service is defined by the type of information (ToI) transmitted (i.e. voice, packet data, control packet, etc.) and by the quality of service (QoS) required. Generally speaking, the quality of service (QoS) of a particular type of service (ToS) is dependent upon the errors encountered over the communication link, the delays encountered in transmitting the information, and/or the information lost while transmitting over the communications link.
As discussed above, a radio link protocol may provide mechanisms to deal with all type of impairments introduced in the radio link by the physical transmission medium. Thus, error control schemes are currently designed for error detection only, error detection and forward error correction, or error detection and retransmission. Current delay control schemes include expedited delivery, bounded delay or unbounded delay, while loss control schemes may include assured delivery, best-effort delivery, or relay service (no recovery). Current bandwidth conservation schemes may include packet header compression, generic payload compression, or application specific compression, and contention resolution schemes may include randomized backoff interval followed by retransmission, channel reservation, round-robin or priority-based polling or adaptive power stepping followed by retransmission. This list of protocol functions is by no means exhaustive.
Network Layer. The third layer is the network layer which is responsible for routing packets from one network node to another. The network layer takes upper layer data units (packets), adds routing information to the packet header, and passes the packet to the link layer.
Transport Layer. The fourth layer is the transport layer which creates virtual end-to-end connections using network layer addressing and routing capabilities. This layer has a number of functions, not all of which are necessarily required in any given network. In general, this layer is concerned with assembling/reassembling of data units, multiplexing/demultiplexing, end-to-end error correction, flow control, etc.
The Transmission Control Protocol (TCP) shown in FIG. 1b as the transport layer, has evolved over many years of use in the wired local area network (LAN) and wide area network (WAN) arenas. However, many of the algorithms used to optimize the performance of TCP in the wired environment are based on some underlying assumptions about the wired network where the TCP is typically used.
Wired and Wireless Environment
In a wired network the bit errors rates are typically on the order of 10xe2x88x929 or better, and bit errors have a tendency to be random. In general, the transmission medium is considered essentially error-free and TCP packets are lost mainly due to congestion in the intervening routers. Moreover, in a wired system the transmission channel has a constant bandwidth and is symmetrical; therefore, the characteristics of the channel in one direction can be deduced by looking at the characteristics of the channel in the other direction.
Due to the practically error-free environment of the wired networks, it is often easiest to use a common link control protocol and to solve congestion problems by xe2x80x9cthrowing bandwidth at the problemxe2x80x9d, to remove queuing bottlenecks by using higher speed transmission channels.
On the other hand, in a wireless environment, most of the above assumptions are no longer valid. The wireless channel is characterized by a high bit error rate with errors occurring in bursts that can affect a number of packets. Due to fading, due to the low transmission power available to the mobile station and to the effects of interference, the bandwidth of the channel appears to rapidly fluctuate over time resulting in a radio link that is not symmetrical.
In a wireless environment, the amount of bandwidth available to the system is fixed and scarce. Adding bandwidth on the radio link may be expensive or even impossible due to regulatory constraints.
For example, optimizing bulk file transfer in a wired environment is simply a matter of allocating as much bandwidth as possible to the connection. In a wireless environment, part of the bandwidth is used in error correction. It is known that more error correction means less payload, however, more error correction increases the probability of correct delivery without retransmissions. Thus, end-to-end throughput may actually be increased by reducing bandwidth assigned to payload and using the freed bandwidth for error correction.
Wireless network solutions targeted specifically at packet data using the Transmission Control Protocol (TCP) have been proposed but they suffer from a number of problems as they are generic to TCP with no distinction made between the requirements of the different applications that use TCP, and with no knowledge of the capabilities provided by different link and application layer protocols.
Another problem associated with the use of the TCP in a wireless network relates to a link layer which works independently of the TCP layer with no intrinsic knowledge of the control and information packet requirements of TCP. The link layer protocol may use mechanisms e.g. automatic retransmissions of lost or corrupted packets, that either duplicate or interfere with mechanisms used by TCP.
Priority-based queuing algorithms as well as parameter controlled behavior for use by RLPs have been also proposed. Priority-based queuing algorithms for use by RLPs are limited in their applicability to problems that can be solved with different queuing algorithms. Parameter controlled behavior as a means to modify the behavior of an RLP according to the values assigned to input parameters, is limited by initial decisions on which parameters are dynamic and which are not. The fundamental behavior of the RLP can not be changed and therefore, any new functions that require a new set of parametric values may be difficult to introduce. Moreover, application-specific functions can not be easily introduced.
Multimedia Wireless Communications
In the multimedia communications world, different applications have different QoS requirements with respect to bandwidth, delay, assured delivery, etc. Therefore performance of a multimedia protocol can be enhanced by using mechanisms specifically designed to overcome the impairments found in the prior art.
Current second generation (2G) wireless systems are designed mostly to handle voice traffic, with some allowances for circuit-switched data. Later, packet data services were grafted onto the 2G systems but these were uniformly treated according to xe2x80x9cbest effort deliveryxe2x80x9d schemes. The type of RLP (radio link protocol) used in 2G systems is typically based on the generic service(s) available to the MS(mobile station), as for example voice services, packet data services, and/or circuit switched data services. The voice service may use an RLP providing error detection and forward error correction, the packet data service may use an RLP providing error detection and retransmissions, while the circuit switched data service may use an RLP providing transparent bit service.
The introduction of multimedia communications in third generation (3G) wireless systems means the traffic no longer has a set of homogenous characteristics and as a result, many of the protocols for 2G wireless systems suffer from a number of design problems.
Existing wireless implementations define a limited number of RLPs (radio link protocols). The RLP for a connection is currently chosen during the connection setup phase and remains tied to the service category for the duration of the connection. To change the type of RLP, the connection must be terminated and a new connection with a different type of RLP has to be established.
Furthermore, RLP selection is currently based on the type of service (ToS) requested (e.g. voice, best effort packet data) and assumes that all services within a category have the same basic quality of service (QoS) requirements and this does not change over time. An RLP operates independently, without knowledge of the transport protocol or application requirements, and the same RLP remains in effect throughout the life of the connection, even though the requirements of the information flow may change.
Moreover, the current RLPs treat all information the same, assuming the same type of service (ToS) requirements applies to all information elements (IE). For example, in a packet mode connection, control packets that regulate the flow of information should be accorded a higher priority and greater assurance of correct delivery than data packets themselves, but they are presently treated equally. Also, RLPs are typically defined during the standardization process and no provision is made for adding a new type of information flow or a new type of service (ToS) category and its corresponding RLP. With the rapid introduction of new applications into wireless and packet data arenas, these applications may be forced to use an RLP that approximately, but does not quite, fit the application""s service requirements.
Accordingly, there is a need for a providing a dynamic link layer for a multimedia wireless communication system which fits a plurality of type of service (ToS) categories of an application, and is capable to recognize different quality of service (QoS) requirements within a category.
The present invention provides an improved end-to-end quality of service (QoS) for multimedia wireless communications.
According to one aspect of the invention, a radio link system for multimedia communication between a radio access network (RAN) and a mobile station (MS) is provided for establishing a connection under RAN monitoring. A RAN connection of a communication link is used for transmitting an information element (IE) having a particular IE type of service requirements, to a plurality of RAN radio link adapter (RLA) components. Each RAN RLA is associated with a type of service and is capable of adapting the IE to a RAN frame format comprising connection information and RLA information associated with the transmitted IE. A flow analyzer is also provided to monitor the communication link, to procure the IE type of service from the RAN connection, to select a RAN RLA component with a RLA type of service substantially the same as the IE type of service and to dynamically allocate the selected RAN RLA component to the RAN connection.
According to another aspect of the invention, a radio link system for multimedia communication between a mobile station (MS) and a radio access network (RAN) for establishing a communication link between the MS and the RAN under the MS monitoring of the connection, is provided. A MS connection of a communication link is used for transmitting an information element (IE) according to a type of service requirements, to a plurality of MS radio link adapters. Each MS RLA is capable of adapting the IE to a MS frame format for transmission over the communication link to a paired RAN RLA. Both the MS RLA and the RAN RLA are selected in accordance with the quality of service (QoS) requirements associated with the IE.
According to still another aspect of the invention, a method for multimedia communication between a radio access network (RAN) and a mobile station (MS) is provided. A communication link for transmitting an information element (IE) according to a IE type of service requirements from a connection in the RAN to a mate connection in the MS, is initially established. The connection is constantly monitored at the originating end, for detecting the IE type of service requirements for a current transmission operation on the communication link. A plurality of radio link adapters (RLA) are also provided, each RLA associated with a RLA type of service for loading the IE into a RLA frame format comprising destination connection information associated with the type of IE. According to each IE type of service requirements identified, an RLA component associated with the IE type of service identified is dynamically allocated to the originating connection end. The destination connection information contained in the RLA frame includes a connection identifier and an RLA identifier for selecting and allocating at the other end of the connection a second RLA component having the same RLA type of service. Either the RAN or the MS can monitor the communication link.
Advantageously, according to the invention, the dynamic selection of the type of RLA to transport information is performed without having to tear-down and re-create a connection. The transport of the information flow of a specific type of service over the radio link is optimized and an end-to-end quality of service (QoS) is maintained.
The invention uses link adaptation techniques that are specifically tailored to the needs of a particular type of information flow, or of a particular end-to-end transport protocol. The operation of each RLA may be tailored to provide services that closely match the requirements of a specific end user or of a particular information flow, or of a type of service. RLA selection may be based on the end user""s profile, on the type of service selected, on the changing characteristics of the information flow, on the type of information element detected within the flow, and/or on the current conditions of the radio link.
Other aspects and features of the present invention will become apparent to those skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying drawings.